The number of external connections available for an integrated circuit is frequently a limitation, especially for large scale integrated circuits incorporating many circuit functions on a single chip. This limitation causes many constraints on logic design and circuit design of a large scale integrated (LSI) circuit chip. Mini-computer and micro-computer system utilizing LSI integrated circuit microprocessor units (MPU) and associated external random access memory (RAM), read only memory (ROM) and specialized interface adaptor circuits all coupled to a single bidirectional data bus are known in the art. Some of the specialized interface adaptor circuits have a plurality of programmable registers selectable on a particular chip. Direct selection of registers on an interface adaptor chip requires utilization of external pins to provide the necessary binary address inputs. Control input lines are also required to such interface adaptor chips to control the direction of data flow to or from the interface adaptor chip. It is always desirable to eliminate external connections if possible, since the economics of packaging integrated circuits requires as few external pins per circuit function on a chip as possible. When too few external connections are available, needed functions on the chip may have to be discarded, and additional circuitry may be required on the chip to derive a signal which could be more conveniently provided from an external source. This increases the size of the chip, and often requires complex circuitry which requires more chip area and may be more sensitive to various processing parameters and result in lower chip yield and therefore higher product cost.